Conventionally, a driver in a vehicle recognizes current driving situation based on his/her experience and external information such as an accident warning sign posted on a roadside signboard or the like. Recognition of the current driving situation includes an approach toward a high-risk point of a road or the like. However, the driver may be aware of the driving situation only about a frequently-traveled road. On the other hand, an increased availability of a navigation system in the vehicle serves as an enhancement of route selection, thereby providing for the driver an increased chance of travel in a less-frequently-traveled road, in a less-familiar road or the like. In view of the above-described situation, information provision regarding the high-risk point of the road by using a road map displayed on the navigation system is considered as an effective driving support for the travel in the less-familiar road or the like.
The driving situation of the vehicle is experimentally determined by using vehicle operation data and biometric indexes derived from the vehicle and the driver so as to detect the high-risk point on the road. For example, the vehicle operation data such as an operation of an anti-lock brake system and/or acceleration/deceleration of the vehicle is used to determine whether the vehicle is making a sudden stop. The vehicle passing the high-risk point may also be detected and determined based on biometric data of physical status, because the driver typically shows a characteristic response when the vehicle is passing the high-risk point. For example, a sudden increase of driver's heat rate may be an indication of the high-risk point even when the vehicle operation data does not show any abnormality.
Japanese patent document JP-A-2003-123185 discloses a technique that utilizes various sensor outputs to determine high-risk situations in driving, and serves a safety of driving by recording the high-risk points in road map data for later use. In this case, the high-risk situations includes abrupt steering, sudden braking, steep acceleration, skid, possibility of rear-end collision, over-speeding, high tension travel, driver's in excitement/tension, an accident prone point, pedestrian/bicycle warning, motor cycle warning, oncoming traffic, succeeding vehicle, low visibility, steep curve or the like.
However, the high-risk situation experienced at a specific point of the road has relevance to various factors such as a driver's skill, surrounding conditions of the vehicle that are arbitrarily given at the time of driving. Therefore, the driver may not catch a point of the warning message even when the pedestrian/bicycle warning is provided for the driver prior to the approach to the high-risk point. That is, the warning message may not be effective nor sufficient for the driver in terms of coping with the high-risk situation.